Preheat oven to 350°F. If you'd like to do a 4 layer cake, grease and line 4 6-inch cake pans with parchment paper. If you'd prefer a 2 layer cake, grease and line 2 8-inch cake pans with parchment paper.
In a large bowl, whisk together sugar, cocoa powder, flour, espresso powder, baking soda, baking powder, and salt. In a separate bowl, whisk oil, eggs, and buttermilk.
Pour the wet ingredients into the dry, whisking until no lumps remain. Pour in brewed coffee, mixing until just combined.
Pour batter into prepared pans and bake for 25 mins (the time should be the same for both cake pan sizes), or until a knife inserted in the center of the cake comes out clean. Cool completely on a wire rack before frosting.
To make the frosting, place butter in a standing mixer fitted with a paddle attachment (an electric hand mixer also works). Cream the butter on high speed for 1 minute, then turn speed to low and add in cocoa powder. Mix until combined, then add in powdered sugar, espresso powder, and brewed coffee. Beat until combined.
Frost cake by placing first cake layer onto a cake stand and topping with a healthy dose of frosting. Spread evenly, then repeat with two additional layers. On the top layer, use a little less frosting. Then, use the remaining frosting to create a thin layer on the sides of the cake, using a blunt knife to spread evenly. Place into fridge or freezer while you make the ganache.
To make the ganache, heat the cream over a double boiler on low heat. Once the cream is scalding (near boiling but not boiling), remove from heat and stir in chocolate. Drizzle ganache over the cake's edges, then over the entire top, again using a blunt knife to smooth things over evenly.